The European Commission is reportedly investigating whether Apple is using anticompetitive sales tactics to muscle out rival handset makers.

While no formal investigation has been announced, European regulators sent a nine-page questionnaire to several European wireless carriers last week to determine whether Apple's distribution terms ensure that competitors can't secure better sales deals, according to documents obtained by the Financial Times. The interest was reportedly spurred by wireless carriers' private complaints that Apple's agreements squelched competition.

The questionnaire focuses on whether Apple's terms mandate a minimum iPhone purchases and whether technical restrictions prevent the iPhone 5 from being used on high-speed 4G networks in Europe, according to the newspaper.

"The Commission has information indicating that Apple and Mobile Network Operators ('MNOs') have concluded distribution agreements which may potentially lead to the foreclosure of other smartphone manufacturers from the markets," the questionnaire states.

"There are also indications that certain technical functions are disabled on certain Apple products in certain countries in the EU/EEA. If the existence of such behaviour were to be confirmed, it might constitute an infringement of [antitrust law]," it says.

The European Commission previously confirmed that it was examining the deals but cautioned that it has not begun an official antitrust investigation.

People with knowledge of Apple's contracts with the carriers say the terms they must accept are unusually strict, especially for smaller carriers, making it difficult for other handset makers to compete. Apple typically sets quotas for how many iPhones its carriers must sell over a certain period.

CNET has contacted Apple for comment and will update this report when we learn more.

Carriers reportedly have until June 17 to respond to the questionnaire.